The present invention relates to intracellular receptors, and ligands therefor. In a particular aspect, the present invention relates to methods for the modulation of processes mediated by invention receptors, as well as methods for the identification of compounds which effect such modulation.
Nuclear receptors constitute a large superfamily of ligand-activated transcription factors. Members of this family influence transcription either directly, through specific binding to the promoters of target genes (see Evans, in Science 240:889-895 (1988), or indirectly, via protein-protein interactions with other transcription factors (see, for example, Jonat et al., in Cell 62:1189-1204 (1990), Schuele et al., in Cell 62:1217-1226 (1990), and Yang-Yen et al., in Cell 62:1205-1215 (1990)). The steroid/thyroid receptor superfamily includes receptors for a variety of hydrophobic ligands including cortisol, aldosterone, estrogen, progesterone, testosterone, vitamin D3, thyroid hormone and retinoic acid, as well as a number of receptor-like molecules, termed xe2x80x9corphan receptorsxe2x80x9d for which the ligands remain unknown (see Evans, 1988, supra). These receptors all share a common structure indicative of divergence from an ancestral archetype.
Identification of ligands for orphan receptors presents a significant challenge for the future since the number of orphan receptors which have been identified far exceeds the number of receptors with known ligands. Indeed, at least 40 genes, both vertebrate and invertebrate, have been identified which are structurally related to the steroid/thyroid receptor superfamily, but whose ligands are unidentified. Among these are Drosophila genes of known developmental significance including: the gap gene, knirps (Nauber et al., in Nature 336:489-492 (1988), the terminal gene tailless, involved in patterning the head and tail regions (Pignoni et al., in Cell 62:151-163 (1990), seven-up, which influences photoreceptor cell-fate (Mlodzik et al., in Cell 60: 211-224 (1990), and ultraspiracle, a gene required both maternally and zygotically for pattern formation (Oro et al., in Nature 347: 298-301 (1990)).
The identification of important Drosophila developmental genes as members of the steroid/thyroid hormone receptor superfamily suggests that vertebrate orphan receptors will have important developmental functions. Furthermore, the identification of ligands for orphan receptors could lead to the discovery of novel morphogens, teratogens and physiologically important hormones.
In accordance with the present invention, we have identified new members of the steroid receptor superfamily of receptors, a representative member of which has been designated XOR-6. Invention receptors are responsive to hydroxy, mercapto or amino benzoates, and are expressed, for example, in Xenopus laevis embryos. XOR-6 is most closely, although distantly, related to the vitamin D3 receptor (VDR). The proteins are about 73% identical in amino acid sequence in the DNA-binding domains and about 42% identical in the ligand binding domain. Like VDR, XOR-6 has an extended D region between the DNA and ligand binding domains. Notably, the region amino-terminal to the XOR-6 DNA-binding domain is extremely acidic. This may influence its ability to activate target genes. XOR-6 is not restricted to Xenopus because southern blots show the presence of XOR-6-related sequences in a variety of other vertebrates. Indeed, a human genomic clone for an XOR-6 related gene has recently been isolated.
In accordance with a particular aspect of the present invention, there are also provided nucleic acid sequences encoding the above-identified receptors, as well as constructs and cells containing same, and probes derived therefrom. Furthermore, we have also discovered that hydroxy, mercapto or amino benzoates modulate the transcription activating effects of invention receptors.